Airbreathing Slush LH2 propellant rocket stage. Aerospaceplane to compete with American X-30. Single stage to orbit, scramjet air breather. Tupolev assigned to start work in 1993. Mockup built, and some subscale flights to Mach 6 on tactical missiles of scramjet model, but project now dormant due to lack of funds. Wing area 160 square meters, wing sweep 70 degrees. Two crew.